Nickel alloy



Patented Jan. 1, 1935 UNITED STATES PATENT OFFICE NICKEL ALLOY Wilhelm Kroll, Luxemburg, Luxemburg, assignor to Siemens & Halske,

Aktiengesellschaft,

Siemensstadt, near Berlin, Germany, a corporation of Germany No Drawing. Applicati on March 3, 1931, Serial 7 No. 519,904. In Germany March 8, 1930 7 Claims.

metal in an amount less than 10 per cent of the weight of nickel and with carbon in an amount less than 1 per cent of the weight of the nickel, said' composition usually possessing a hardness produced by heat treating and ageing after compounding; and it further comprises a process of producing a hard nickel alloy of high tensile strength wherein a nickel alloy containingsmall percentages of carbon and of an alkaline earth metal or lithium is heated to a high temperature, suddenly quenched, and then kept at a moderately high temperature for an extended period of time; all as more fully hereinafter set forth and as claimed.

In the art are known various alloys of nickel, cobalt or copper with beryllium; which alloys it is possible to improve for various useful purposes by heat treatment. In particular, the hardness of such alloys is increased by heating them to comparatively high temperatures and cooling to lower temperatures with subsequent annealing treatments. It has also been proposed to add other elements to such alloys in amounts which result in substantial reduction of the content of beryllium required in the finished alloy. Beryllium appears to have the power of imparting to the alloy the property of hardening under such heat treatment. Beryllium is one of the rarer metals.

I have discovered that certain other and more available metals, upon being alloyed with commercial nickel permit of improvement of the alloy by heat treatment. The metals which I have found particularly beneficial in this relation belong to a group of metals which may be designated as base-forming. To this group belong lithium and the alkaline earth metals, namely, calcium, strontium, barium and magnesium, the latter metal being classed for present purposes as an alkaline earth metal. For example, an alloy made in any of the known ways from commercial nickel and small proportions of magnesium, of an order between 0.5 and 10 per cent can be given a large increase in hardness measured in Brinell number by heating to around 1050 C. and quenching to about 500 C. with subsequent heat treatment at the latter temperature for 12 hours. I have found for instance that the hardness of the alloy is increased bythis treatmentfrom an initial value not substantially below 130 Brinell to a final value of about 250 Brinell. The alloys of nickel with the other alkaline earth metals and with lithium in like small amounts are likewise capable of being improved in hardness and in tensile strength by a simple heat treatment. For example, the increase of hardness in a nickelcalcium alloy containing 1 per cent calcium, when employing treatment as above outlined, amounts to about 40 Brinell, that for a nickel-lithium alloy with about 1 per cent lithium to about 70 Brinell. The percentage of the alloying metal required to bring about the increase of hardness upon the heattreatment is quite small. Advantageously, its percentage is kept at not over 10' per cent of the weight of the alloy or of the weight of the nickel.

I havealso discovered that an additional benefit by way of increased hardness and increased tensile strength is obtained when, in addition to one or more of the above-named group of baseforming metals, the nickel contains a small percentage of carbon, say, not more than about 1 per cent of the weight of the nickel. I have found that when the alloy containing the baseforming metal is made from nickel containing some such small percentage of carbon and when the heat treatment is efiected with exclusion of air, an extraordinarily large increase of hardness may be obtained in such alloys.

Another feature of my invention is in coordinating to each other the content of the carbon and of base-forming metal so that a certain content of carbon is associatedwithacertainadditionof magnesium, for example, in order to obtain increased hardness and structural strength in the finished alloy. Alloys with 1 per cent of carbon and 10 per cent of magnesium are susceptible of hardening by the heat treatment, but ordinarily carbon is employed in amounts as low as 0.10 to 0.20 per cent and the content of magnesium is usually between 0.8 to 1.8 per cent. A useful composition of an alloy for hardening under heat treatment contains magnesium 0.50 per cent, carbon 0.10 per cent. Such an alloy has, in a rolled state after quenching from 1050 C., a hardness of 121 Brinell and a tensile strength of 59 kg. per square millimeter at 38 per cent elongation. Upon 24 hours heat treating at 500 C. after quenching from 1050 C., the tensile strength increased to 108 kg. per square millimeter at 10 per cent elongation.

In a further typical embodiment of my invention, a nickel-magnesium alloy containing 1.8 per cent of magnesium and 0.02 percent of carbon, the balance of the alloy being nickel, upon quenching and subsequent ageing under heat treatment, increases in hardness by 32 per cent above the initial value. Another alloy with 0.53 per cent of magnesium and 0.20 per cent of carbon increases its hardness by 155 per cent above the initial value, namely, from 129 to 330 Brinell. It may be mentioned here that nickel containing carbon alone, without the alloying base-forming metal is practically incapable of being improved in hardness and tensile strength by heat treatment, although nickel at 1300 C. takes up 0.5 per cent carbon in stable solution and at room temperature only 0.17 per cent. When however the base-forming metal, and particularly magnesium, is added to nickel containing carbon in amounts which may be below 0.17 per cent a pronounced hardening efiect is produced by quenching and ageing.

The most favorable quenching temperature is about 1100 C. but good results are obtained at temperaturesas low as 750 C. and increase of the quenching temperature to 1350 C. still gives useful results. The most favorable heat treating or ageing temperature is around 500 C. with a period of treatment of 24 hours, but good effects are also obtained at 380 C. If a temperature above.500 C. is used in ageing, it-is advisable to shorten the time of heat treatment.

I have also ascertained that the same improvement inproperties as described above is obtained by similar additions of the named base-forming metals to nickel alloys containing copper,

. that the hardness and tensile strength are increased by a heat treatment of alloys of nickel with such elements as aluminum, boron, cerium, chromium, cobalt, iron, copper, manganese, molybdenum, silicon, tantalum, titanium, vanadium, tungsten, zinc and tin, to which have been added one or more of the base-forming metal.

group. In quantity, the proportion of these 'alloying elements may be as high as 45 per cent by weight of the finished alloy.

By the expression balance substantially nickel occurring in the claims, I means that the alloys called for may also contain in addition to nickel small proportions of the metals enumerated above in proportions insufllcient to substantially change the nature and characteristics of these alloys.

In the case of an addition of silicon, in particular, a slight improvement in the hardening capacity could even be observed. Various of the metals named, in particular tantalum, molybdenum, chromium, silicon and tungsten, act favorably on the corrosion resistance of these alloys. Of importance are, in particular, the nickelchromium and the nickel-chromium-iron alloy which become highly susceptible to heat'treating by an addition of magnesium and carbon. In-

stead of magnesiumother alkaline-earth metals or lithium may be employed. The hardening capacity of such alloys is of particular importance if they are to be employed for the manufacture of high-speed tools, hammers and the like.

What I claim is:

1. A heat-hardened beryllium-free nickel alloy comprising at least one base-forming metal in proportions ranging from a small but effective amount up to about 10 per cent and selected from a group consisting of lithium, calcium, strontium, barium and magnesium, and also comprising about 0.05 to 1 per cent of carbon with abalance substantially nickel, and having the structure, hardness and other properties produced by quenching said alloy from temperatures of about 750 to 1350 C. followed by prolonged heating at temperatures from about 380 C. to 500 C.

2. A heat-hardened beryllium-free nickel alloy comprising from about .5 to about per cent of at least one base-forming metal selected from a group consisting of lithium, calcium, strontium, barium and magnesium, and from about 0.05 to 1 per cent of carbon with a balance substantially nickel, and having the structure, hardness and other properties produced by quenching said alloy from temperatures ranging from about 750 to 1350 C. followed by prolonged heating to temperatures from about 380 C. to 500 C.

3. The alloy of claim 1 wherein the base-forming metal is calcium.

4. The alloy of claim 1 wherein the base-forming metal is strontium.

5. The composition of claim 1 wherein the baseforming metal is magnesium.

6. The composition of claim 2 wherein the baseforming metal is magnesium.

'7. A heat-hardened beryllium-free nickel alloy comprising from about 0.8 to 1.8 per cent of magnesium and from about 0.05 to 0.2 per cent of carbon with a balance substantially nickel, and- 

